1. Technical Field
Aspects of the disclosure relate to a fixing device that thermally fuses a developer image transferred to a recording sheet.
2. Description of the Related Art
A fixing device including a cylindrical fusing film, a heater disposed inside the fusing film, and a heating plate (nip plate) that forms a nip portion between the heating plate and a pressure roller with the fusing film therebetween is known as a fixing device used in an electrophotographic image forming apparatus. In this fixing device, a sheet of paper is conveyed through the nip portion between the fusing film supported by the nip plate and the pressure roller, and a developer image on the sheet is thermally fused in the nip portion.
Such a conventional fixing device may change the state of the nip portion (hereinafter also referred to as “nip state”), such as the pressure in the nip portion (hereinafter also referred to as “nip pressure”) and the width of the nip portion (hereinafter also referred to as “nip width”), for the purpose of suitable thermal fixation to sheets with different thicknesses, such as sheets of plain paper and heavy paper, and removal of a sheet jammed in the nip portion. A structure for changing the nip state is, for example, a structure that moves only the nip plate toward and away from the pressure roller.
However, in the case of such a structure that moves only the nip plate toward and away from the pressure roller, the clearance between the nip plate and the heater needs to be large to prevent the nip plate from coming into contact with the heater that does not move relative to the pressure roller. This increases the size of the fixing device.